The present invention relates to a device for feeding yarn with a constant adjustable tension, for use in weaving looms and in other weaving machines, wherein important improvements have been introduced in the means for braking the outcoming yarn.
The yarn feeding device to which the present invention refers is of the type comprising a substantially cylindrical body or drum, onto an end of which are wound the turns of the yarn to be fed by means of a winding arm, the turns being then led axially forward by suitable means and being unwound at the opposite end by the weaving machine, particularly a weaving loom.
The tension of the unwinding yarn is controlled by braking means adapted to guarantee a constant and even tension when the machine is working.
In the so far known devices of this type, the tension of the unwinding yarn is controlled by braking means which often consist of a brush cooperating with the outer base of the cylindrical body or winding drum from which the yarn unwinds and which is mounted on a suitable external support.
The brush consists of a circular ring from which project, either in continuous form or arranged in bundles, more or less long bristles--usually of synthetic material--having a constant or variable inclination, for the purpose of obtaining an adjustment of the yarn tension.
However, an increased or reduced pressure of the brush on the drum of the feeder keeps the adjustment of the yarn tension within rather limited ranges, while the bristles of the brush get quickly worn, especially when working with abrasive yarns, and the brush itself undergoes a certain deformation, especially if one tries to obtain a high tension, as required for thick yarns; finally, the bristles of the brush become inpregnated, when working with yarns which deposit along their path the substances with which they have been previously treated during the spinning operations.
The consequence of all these inconveniences is an irregular tension of the outcoming yarn. It so happens that, in most cases, the brush braking means are merely used to stop or limit the forming of balloons in the unwinding yarn, and that the function of adjusting the tension is then performed by other means.
Other known braking means in the yarn feeding devices provide for the use of a plurality of substantially radial elements of thin sheet-metal, which are elastically pressed against the outer base of the winding drum in order to adjust the tension of the unwinding yarn.
In such braking means, the sheet-metal elements are retained at the ends between a ring and a hub of plastic material, said ring and said hub being also connected by radial elastic laminae.
These means practically eliminate all the drawbacks of the brush brakes; however, since they act substantially in a radial sense, they have the inconvenience of having their contact area with the outer base of the cylindrical winding body generally about a circumference which has a far smaller diameter than that along which the winding of the yarn turns takes place, it being appropriate for the rim of the winding body to comprise a wide fillet between the lateral surface and the base of the cylinder itself. This very much limits the action of stopping the balloon of unwinding yarn, which such means are adapted to accomplish. Moreover, in those feeding devices wherein the direction of advancement of the turns is the same as the direction of movement of the outcoming yarns, the use of radial sheet-metal braking means forces the outcoming yarn to deflect through a total angle of more than 180.degree., in order to pass from the cylindrical winding body onto the axis along which the yarn gets drawn, thereby subjecting the yarn itself to a higher stress compared to the other known brush braking means, where said angle does not usually exceed 90.degree..